The present invention relates to the controlled production of aluminum chloride and silicon chloride in the carbo-chlorination of kaolinitic ores. Kaolinitic ore is defined as an ore containing a substantial proportion of kaolin. More specifically, the instant invention is primarily concerned with the rapid and preferential carbo-chlorination of alumina over silica in the kaolinite in the ore, by controlling the levels of boron chloride and reductant present during the carbo-chlorination step.